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How Does DNA Copy Itself? 12.3 DNA Replication

How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

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Page 1: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

How Does DNA Copy Itself?

12.3 DNA Replication

Page 2: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication – What and Why

Replication = DNA making copies of itself– DNA must be copied before a cell can divide– Each new cell will have

a complete set of DNA

Page 3: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

History of Replication

Watson & Crick – realized that

complementary base pairing

provided a way for DNA to copy itself

- base pairing could allow a new

strand to be built on an old strand

- 3 possible models of DNA

replication

Page 4: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

3 Models of Replication: Semi-conservative Replication

Each strand in a DNA molecule

is used as a template to build

a new strand using

complementary base pairing Results in new molecule

with one original DNA strand

and one new strand

Page 5: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

3 Models of Replication: Conservative Replication

Leaves the original DNA

intact and produces another

molecule of DNA identical to

the first

Page 6: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

3 Models of Replication: Dispersive Replication

Creates two molecules that

are a mix of new and old DNA

interspersed along each

strand of the molecule

Page 7: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

The Question is Answered

1957 Matthew Meselson & Franklin Stahl

-conducted an

experiment proving

replication is

semiconservative

- each DNA molecule

has one new strand

and one old strand

Page 8: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication: Process

@Replication begins when the enzyme DNA helicase opens the DNA forming replication bubbles@

Page 9: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication: Process

Multiple replication bubbles are opened simultaneously allows the molecule to be replicated quickly

Page 10: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication: Process

The nitrogen bases

on the original DNA

strands are exposed

in the replication

bubbles. They serve

as a template to

build new DNA

strands

Page 11: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication

The ends of the replication bubbles known as the

replication fork is where replication begins

Page 12: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication – DNA Polymerase

@The enzyme DNA polymerase brings new nucleotides to the

replication fork@

- it pairs them according to base pairing rules A pairs with T

C pairs with G

Page 13: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication – Leading Strand

The process of replication

proceeds from 5’ to 3’ leading strand- replication

is continuous

– it is built toward the replication fork

Page 14: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication – Lagging Strand

lagging strand- replication

occurs in short segments

- called Okazaki fragments

- the new DNA strand grows

away from the replication

fork

Page 15: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication- The Big Picture

Each Bubble has 2 Forks – each fork has a leading and lagging strand

Page 16: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication

The process continues until 2 complete copies of the DNA are produced

@Each copy of the DNA has 1 strand of DNA

from the original DNA and one new strand that was produced by replication@

Known as semi-conservative replication

Page 17: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

DNA Replication

Page 19: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

Telomeres

– The tips of chromosomes are known as telomeres.

– Over time, DNA may actually be lost from telomeres each time a chromosome is replicated.

– @An enzyme, telomerase, solves this problem by adding short, repeated DNA sequences to telomeres@

Page 20: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

Prokaryotes vs. Eukaryotes

Prokaryotes- starts from a single point and goes in two directions until the entire chromosome is copied.

Eukaryotes- replication begins at dozens or even hundreds of spots on the DNA, going in both directions until each chromosome is completely copied.

Page 21: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

Which enzyme is used to separate the DNA?

A. Helicase

B. Ligase

C. Polymerase

D. Telomerase

Page 22: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

Which enzyme adds nucleotides to the strands?

A. Helicase

B. Ligase

C. Polymerase

D. Telomerase

Page 23: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

Which enzyme prevents DNA from being lost during replication?

A. Helicase

B. Ligase

C. Polymerase

D. Telomerase

Page 24: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a

How is Prokaryotic DNA different from Eukaryotic?

Prokaryotic DNA is circular and replication begins at 1 point.

Eukaryotic DNA is linear and replication begins at many points.